A vehicle's suspension system plays a vital role in both serving to isolate the occupants of the vehicle from the irregularities of the road surface, and helping to control the stability of the vehicle by managing the relative position of the wheels to the vehicle body during the vehicle's operation. Suspension systems are divided into two main categories, dependent and independent, terms which refer to the ability of the opposing wheels (i.e., the wheels on the same axle) to move independently of each other. In general, with a dependent suspension, the movement of one wheel affects the orientation of the opposing wheel. An independent suspension, on the other hand, allows one wheel to move freely and unhindered by the opposing wheel, thereby allowing the wheels to react individually to the bumps and dips in the road surface. An independent rear suspension (IRS), for example, allows for the rear wheels of the vehicle to be independently sprung.
IRS systems can also take various forms, including, for example, a double wishbone suspension, a multi-link suspension, and an integral link suspension. A double wishbone suspension, for example, has two sets of lateral “A” arms, which are generally called upper and lower control arms, and toe links. Each control arm has two attachments to the body and a single attachment to the steering knuckle (or wheel carrier). The three knuckle attachments (upper arm, lower arm, and toe link) on each side establish the plane of each wheel and control both camber angle and toe angle while reacting to wheel loads. Each side is separate from the other half which serves to independently isolate the reaction of each wheel to the road surface.
A more refined form of the double wishbone suspension is the multi-link suspension, which conceptually separates the structural performance of each “A” arm into two tension/compression links. Thus, a conventional 5-link suspension system can be thought of as separating the upper control arm into an upper trailing link and a camber link, separating the lower control arm into a lower link arm and a spring link, and retaining the toe link. The orientation and length of each link governs the suspension's geometric performance as well as the magnitude of link loading when wheel forces are reacted.
An integral link suspension connects a steering knuckle to an isolated sub-frame by means of a lower control arm, a camber link and a toe link. The steering knuckle is directly connected to the lower control arm via a pivot point and indirectly via an additional link, the integral link. The integral link may, for example, decouple caster compliance from longitudinal compliance, thereby preventing the need for a trailing link or control blade. An integral link rear suspension is, therefore, softer in wheel recession rate vs. the conventional 5-link suspension, stiffer in caster stiffness vs. the conventional 5-link suspension, and allows for a lower rear body rail package for increased interior volume (since the upper trailing link is eliminated). Accordingly, the integral link suspension may provide a substantial reduction in cruising interior noise, while also significantly improving impact harshness and aftershake, as compared with the conventional 5-link suspension, while not compromising vehicle handling.
Although an integral link suspension system has various advantages over the conventional 5-link suspension system, a conventional integral link suspension typically costs and weighs significantly more than the 5-link suspension (which utilizes a compilation of relatively light and inexpensive two-force members) often making its use not feasible for standard applications.
It may, therefore, be advantageous to provide an IRS system that functions like an integral link suspension system (which provides the advantages of the integral link system vs. the conventional 5-link system), while having a cost and weight similar to that of the conventional 5-link system.